Widespread use is made in the electrical and electronics industries of substrates having conductors on one or both of their surfaces. The substrates may comprise relatively thin films, such as Mylar (polyester) or Kapton (polyimide). The conductors are provided on the surfaces of the films by several different methods. Silkscreening is widely used as a low cost method of producing extremely thin conductors on the surfaces of the films. Silkscreened conductors are extremely delicate, or fragile, and are subject to damage when electrical connections are made to such conductors. Conductors are also provided on surfaces of films by electrodeposition in selected areas and along desired conductive paths, or by depositing conductive metal over the entire surface of a film and selectively etching the surface to leave the desired conducting paths. These electrodeposited conductors are somewhat more durable than silkscreened conductors but are still relatively fragile. It is also known to laminate thin sheets of conductive metal to a film and etch away the surface of the film to leave the desired conductors. These laminated wrought metal conductors are relatively durable and relatively thick, but they are also relatively costly to produce.
Electrical connections can be made to conductors on insulating films by soldering methods, but these are usually highly labor intensive and therefore costly. Furthermore, care must be taken in making soldered connections to silkscreened and electrodeposited conductors that the conductors on the film will not be damaged by the heating of the soldering operation. Several crimp-type connecting devices can be used on laminated film having wrought conductors thereon, see for example U.S. Pat. No. 3,395,381. However, while wrought conductors on film will withstand the relatively high compressive forces required during the crimping operation, the more delicate electrodeposited and silkscreened conductors are liable to be damaged by these compressive forces during the crimping operation.
The present invention is directed to the achievement of a crimped electrical connection which can be used with all types of conductors on films; wrought laminated conductors, silkscreened conductors, and electrodeposited conductors. The invention is further directed to the achievement of a crimping method which does not cause damage to relatively fragile conductors.
A crimped electrical connection in accordance with the invention is produced by initially forming a strip of conductive metal into a "U" and positioning the film between the arms of the "U" with the conductor on the film in alignment with one of the arms. The U-shaped connecting device is then located between the opposed parallel faces of crimping dies and the dies are moved towards each other in a direction extending normally of their opposed faces. As the dies are closed, the arms of the U-shaped connecting device, which function as cantilever beams, first move towards each other until their ends engage the surfaces of the film. The opposed surfaces of the dies are moved an additional distance towards each other and during such movement, they reduce the crimp height of the bight portion of the connecting device with accompanying plastic or permanent deformation of the bight portion. During movement of the dies for this additional distance, the arms of the cantilever beams are resiliently flexed against the surfaces of the film so that permanent electrical contact is established with the conductor on the film. A particularly significant feature of the invention is that during the final stages of crimping, the principal crimping forces are applied only to the bight portion and not to the cantilever beams. The conductors on the film are not therefore subjected to these high principal crimping forces, but they are subjected to much lower forces which are developed in the cantilever beams.